Trees of New York State 49 



B. Leaf-soars and Stipule-scars 



Leaf-scars are the scars on twigs which result from leaf-fall 

 and of necessity have the same arrangement as leaves. (Fig. 67.) 

 As pointed out in previous paragraphs, the fall of leaves in 

 deciduous species is a normal physiological process for which 

 nature makes preparation some days in advance. Leaf -scars vary 

 greatly in contour, size, and elevation ahove the surface of the 

 twig and are important features in twig identification. They 

 vary widely in shape from narrowly V-shaped, linear, or lunate 

 to semicircular, cordate and elliptical. The narrow forms may 

 extend nearly or quite around the twig while the broad forms 

 are usually confined wholly to one side. The size varies greatly 

 in different kinds of trees. Trees with stout twigs, as Ailanthus, 

 are usually characterized by large leaf -scars, while in other forms 

 with slender twigs like some of the cherries, they are so small 

 a^ to render them difficult of detailed observation without a 

 pocket lens. Where leaf-scars are elevated above the surface of 

 the twig owing to the elevation of the absciss layer, they are said 

 to be decurrent on the twig, an expression which has been coined 

 to indicate the somew^hat fluted appearance of the twig immedi- 

 ately beneath the leaf-scar. Leaf-scars remain visible on twigs 

 for a number of years but eventually slough off as new bark is 

 formed beneath them by the enlarging branch. 



On many tw-igs leaf-scars are accompanied by stipule-scars 

 (Fig. 68) w^hich are inserted laterally to the leaf -scars and assume 

 various shapes. In other cases stipules are either wanting or 

 speedily fugacious and leave no permanent traces on the stem. 

 Where present, stipule-scars, like leaf-scars, vary in contour and 

 may be triangular, semi-circular, etc. In trees like the Sycamore 

 (Fig. 68) they extend around the stem obliquely and meet in a 

 point on the back. Stipular thorns are features of the winter 

 twigs of certain species and offer a ready means of identification. 



C. Vascular bundle scars 



Vascular bundle-scars, generally termed "bundle-scars," are 

 found included in the boundaries of leaf, stipule, and "growing 

 ■point-scars". (Figs. (17 and 68.) In stipule-scars they are 

 generally so minute and indistinct as to be of no diagnostic value 

 whatsoever. "Growling point-scars," that is, the scar resulting 

 from the sloughing off' of the growing point in woody plants of 

 determinate growth, have vascular scars which are circular in 



